This invention relates to novel wholly aromatic copolyamides synthesized from N,N'-bis(4-aminophenyl)isophthalamide as a starting compound. More particularily, the invention relates to aromatic copolyamide polymers prepared from a mixture of p-phenylenediamine and N,N'-bis(4-aminophenyl)isophthalamide as aromatic diamines. 2. Description of Prior Art
Aromatic polyamides having a high melting point and glass transition temperatures are characterized by the outstanding physiochemical and mechanical characteristics such as high thermostability, chemical resistance, and elasticity. Fibers prepared from the aromatic polyamides having the above characteristics can be used as high heat resistant fibers, reinforcing agents for rubbers, composite materials or the like. Particularly, fibers having ultrahigh tenacity and elasticity can be prepared using poly(p-phenyleneterephthalamide) as a polyamide or copolyamide with the molecular chain extended from both ends of the aromatic ring toward its parallel direction. As a representative example of such fiber consisting of poly(p-phenyleneterephthalamide), "Kevlar" is generally well known aramid fiber which is commercially available from E. I. Du Pont de Nemours and Company, Wilmington, Del., U.S.A. However, in spite of the above outstanding characteristics of the aramid fiber, this prior art process has been encountered with difficulties due to the significantly low solubility of p-phenyleneterephthalamide in the polymerization solvent.
A poly(p-phenyleneterephthalamide) must be dissolved in very limited kinds of polymerization solvents such as strong sulfuric acid or a mixture of hexamethylphosphoramide and N-methylpyrrolidone to which mixture LiCl is added. Practically, the strong sulfuric acid is only available as a solvent used in the process for the preparation of the spinning solution which forms lyotric liquid crystals. When this polyamide is applied to industries, a lot of troubles may occur from the use of the strong sulfuric acid, such as corrosion onto the installations, dangers in handling, difficulties in removing the remnant solution and complexity in dissolving polymers in the solvent. Especially, the fibrillation of the fibers due to the use of the sulfuric acid may cause fatal drawbacks in the conventional use of the fibers. The fibrillation into a number of individual fibrils is ascribed to the sudden deletion of the sulfuric acid between the molecular chains, at the time the coagulation occurs in the polymerization solution for the formation of the fibers. Thus, these severe drawbacks found in the aramid fiber are caused by the residual sulfuric acid in the fiber, and the fibrillation might result in the restriction of utility of the fiber as an reinforcing material for rubbers or cements.
To increase the solubility of the polyamides or copolyamides as described above, the molecular chains need to be linked at both ends of the aromatic rings. In this connection, it is known that the aromatic ring units are linked at the meta-position or the rotatable bond is introduced into the position between the aromatic rings. This results in the increase of the solubility of the copolyamide in the polymerization solvent.
The polymerization solution so prepared has a high polymerization degree and stable isotropic property which does not cause the phase separation, and gives fibers and films by directly spinning and casting. However, mechanical characteristics such as the elasticity of the fiber greatly decrease with the increase of the proportional ratio of m-phenylene of the formula: ##STR1## in the molecular chain. Likewise, in case of the films, the mechanical characteristics such as transparency also decrease. The deterioration of the mechanical characteristics caused by the procedures to improve the solubility of the copolyamide could not completely overcome even though a lot of efforts have been tried by inducing the modified units into the copolyamide with the molecular chain like rigid rod. Also, the polymerization solution of the copolyamide is so unstable that there are a lot of difficulties to form fibers or films. Therefore, it is too difficult to commercially prepare the copolyamide having high molecular weight.
However, these defects have been overcome by the use of another unit modified from p-methylene of the formula: ##STR2## and a third monomer, as described fully in U.S. Pat. No. 4,075,122. From this patent, it is noted that the fibers and films are prepared by directly spinning and casting, respectively, without the process for the preparation of the spinning solution forming lyotropic liquid crystal. The fiber prepared from the process mentioned above is known as "TECHNORA" commercially available from Teijin Limited, Osaka, Japan. On the other hand, this trial is only valuable in overcoming the defects of the mechanical characteristics. That is, 3,4'-diaminodiphenylether of the formula: ##STR3## used as a third monomer in the process for the preparation of "TECHNORA" is significantly expensive in cost, resulting in economically disadvantage.
Accordingly, the object of the invention is to provide a wholly aromatic copolyamides as novel polymers.
Another object of the invention is to provide fibers and/or films having ultrahigh tenacity, elasticity and thermostability properties.
Yet another object of the invention is to provide a process for preparing a copolymerization solution having better stability and fluidity using a novel diamine monomer.
Still another object is to provide a process for preparing fibers and films by direct spinning and casting the copolymerization solution.
Other objects and advantages of the invention will become apparent from the following description of the invention.